Processing copper base alloys

ABSTRACT

Processing copper alloys to obtain an improved combination of yield strength and elongation and the restoration of high yield properties in formed parts. The process is characterized by cold rolling, followed by heat treating, forming and finally heat treating to restore desired properties.

United States Patent 1 1 Shapiro et al.

[ PROCESSING COPPER BASE ALLOYS [75] Inventors: Stanley Shapiro, NewHaven;

Ronald N. Caron, Branford, both of Conn.

[73] Assignee: Olin Corporation, New Haven,

Conn.

[22] Filed: Oct. 1, 1973 [21] Appl. No.: 402,479

[52] US Cl. 72/364; 148/11.5 R [51] Int. Cl. B2lb 3/00 [58] Field ofSearch 148/11.5 R; 72/364 [56] References Cited UNITED STATES PATENTS2,676,123 4 1954 Gregory ..148/l1.5

[4 1 May 13, 1975 7/1962 Hartmann 148/1l.5 11/1966 Eichelman et a1148/11.5

OTHER PUBLICATIONS Metals Handbook, American Society for Metals. 8thEd., Vol. 2, page 285.

Primary E.raminer-Lowell A. Larson Attorney, Agent, or FirmRobert H.Bachman [57] ABSTRACT 10 Claims, No Drawings PROCESSING COPPER BASEALLOYS BACKGROUND OF THE INVENTION The process of the present inventionis concerned with treating copper base alloys in order to obtain animproved combination of yield strength characteristics and elongationand the restoration of high yield properties in formed parts.

Since most engineering components, springs in particular, must operatein the elastic regime, information regarding the onset of plastic flowin metal systems has long been one of the most important engineeringdesign criteria. The mechanical property of great interest in thisregion is the elastic limit. However, there are practical difficultiesin determining the elastic limit with information from the engineeringtensile test. Since the elastic limit can be as much as ll5 ksi greaterthan the proportional limit, which is the stress at which thestress-strain curve becomes nonlinear in the elastic regime,determination of the elastic limit would require that each tensilespecimen be alternatively loaded and unloaded to increasingly higherloads until that load is reached which produces a permanent set in thespecimen. I

However, the 0.01 percent offset yield strength approximates and isfrequently used in place of the elastic limit in spring design. Thus,for engineering applications in which little or no plastic flow can betolerated an enhanced 0.01 percent offset yield strength would lead toimproved materials utilization and performance. Formed parts, however,will lose a portiion of the yield properties and it is naturallydesirable to be able to restore high yield properties.

Accordingly, it is a principal object of the present invention toprovide a process for obtaining improved yield strength characteristicsin copper base alloys, particularly high 0.01 percent offset yieldstrength and restore high yield properties in formed parts.

A further object of the present invention is to provide a process asaforesaid which is suitable for manufacturing parts while allowingretention of the desired high yield strength properties.

A further object of the present invention is to provide a process asaforesaid which is simple, inexpensive, easily practiced commerciallyand versatile.

Further objects and advantages of the present inven tion will appearhereinbelow.

SUMMARY OF THE INVENTION In accordance with the process of the presentinvention it has been found that the foregoing objects and advantagesmay be readily obtained. The process of the present invention comprises:

A. providing a copper or copper base alloy material in plate form havinga thickness of from 0.300 to 1.800 inches;

B. cold rolling said material to a total reduction of at least 65percent and preferably more than 85 percent, said cold rolling may beaccomplished directly or by cycles of cold rolling with an intermediateheat treatment between each cold rolling cycle of from 100 to 350C forfrom 1 to 4 hours, provided that the rolling reduction in each coldrolling cycle is at least 25 percent;

C. subjecting said material to a final heat treatment after coldrolling, said final heat treatment being at a temperature of from 100 to350C for from 30 minutes to 8 hours;

D. forming said material into a desired shape; and

E. heat treating said material at 100 to 350C for from 30 minutes to 8hours to restore high yield properties.

The material produced in accordance with the process of the presentinvention may be readily utilized to manufacture parts having high yieldproperties. We have found that when the part is manufactured, the yieldstrength properties fall off due to the cold work which is given to thepart as a result of the forming operation. Therefore, in accordance withthe process of the present invention a further thermal treatment isperformed on the formed part of a temperature of from 100 to 350C forfrom 30 minutes to 8 hours in order to restore the desirable high 0.01percent offset yield strength properties. Furthermore, it can be seenthat the process is simple and easy to perform and inexpensive in acommercial operation.

Further advantages of the instant process will appear hereinbelow.

DETAILED DESCRIPTION The process of the present invention, as indicatedhereinabove, may be readily utilized with any copper or copper basealloy material. Thus, commercial purity or pure copper may be readilyemployed. A particularly suitable series of copper alloys for use in theprocess of the present invention are the phosphor bronzes, which arecopper base alloys containing from 1 to 10 percent tin, such as CDAcopper alloy No. 505, 510, 521 and 524. In addition, the iron containingcopper alloys containing from 1 to 5 percent iron may be readilyutilized, such as CDA copper alloy 194 and 195. In addition, thenickel-silvers are desirably suitable for use in the process of thepresent invention. These alloys are copper base alloys containing fromabout 10 to 20 percent .nickel and from about 5 to 40 percent zinc, suchas CDA copper alloy No. 762, 752 and 745. A further series of copperalloys which may be desirably utilized include the aluminum-bronzes andbrasses containing from 2 to 13 percent aluminum, such as CDA copperalloy 638 and 688. Naturally, many other copper alloys may be desirablyutilized in the process of the present invention. Generally, any copperbase alloy may be conveniently utilized, such as: the CDA 2XX series,brasses containing from about 5 to 40 percent zinc; copper alloyscontaining beryllium; the CDA 4XX series, tinbrasses containing tin andzinc; silicon bronzes; manganese-zinc containing copper alloys as CDAalloys 669 and 672; and cupronickels containing from about 5 to 35percent nickel as CDA alloys 706 and 715.

The starting material should be a copper or copper base alloy materialin plate form having a thickness of from 0.300 to 1.800 inches. Theplate material may be obtained by any desired method. For example, onemay start from a copper base alloy ingot which is hot or cold rolled toplate thickness. The cold rolled plate may then be annealed to the fullyrecrystallized condition. Alternatively, one may provide a continuouslycast copper base alloy plate as starting material.

The process of the present invention cold rolls the plate to a totalreduction of at least 65 percent or alternatively cold rolls the platematerial in at least two cold rolling cycles to a total reduction of atleast percent,

with an intermediate heat treatment of from 100 to 350C for from 1 to 4hours between each cold rolling cycle. The rolling reduction in eachcold rolling cycle should be at least percent and the total reduction inall cold rolling cycles is preferably greater than percent. Thus, onemay cold roll directly to final gage. Al-

ternatively, one may desirably utilize two, three or four cold rollingcycles with one, two or three intermediate heat treatment steps.

Following the finalcold reduction step, the material is subjected to alow temperature heat treatment at final gage. This heat treatment stepshould be for from 30 minutes to 8 hours at a temperature of from 100 to350C.

In accordance with the present invention the material may be readilyformed into a desired shape from the thermally treated strip.Conventional forming operations may be employed, such as stamping,drawings, stretching or bending. We have found that formed parts lose aportion of the desirably high yield properties due to the cold workwhich they have been subjected to. In order to restore the high yieldproperties, the formed parts are given a further low thermal temperaturetreata marginal strength loss in order to enhance cold 'rolla' I lbility for the additional cold rolling steps and for subse quent formingof the final material.

The process of the presentinvention andadvantages obtained thereby maybe readily understood from a consideration of the following illustrativeexamples.

EXAMPLE 1 A copper base alloy ingot. was provided having the I 7following composition: tin, 4.4 percent; phosphorus, 0.07 percent;balance essentially copper. The ingot was Y '7 initially hot rolled andmilled to 0.600 inchgageand after each cold reduction of 250C for 2hoursto'recover the properties lost by the forming operation. The Itensile properties were determined after each process. ing step in boththe longitudinal (rolling) and transverse directions as indicated inTable I below). i I

TABLE 1 Strengths in ksi I I I Material 0.01% I 0.1% 0.2% UltimatePercent Yield Yield Yield Tensile Elongation Strength Strength StrengthStrength: I ff Transverse g 1 CR 96.7% 89 117 128 148 2.8 250C-2 Hours97 118 124 131 5.0 CR 2.4% 86 112 122 137 4.4 250C-2 Hours 102 122 128133 6.2 CR 4.4% 86 114 124 140 V I 4.6. 250C-2 Hours 97 118 124 130 6.7CR 6.8% 90 116 125 139 i 4.7. 250C-2 Hours 96 118 124 129 l 4.8Longitudinal I g 1 CR 96.7% 82 113 123 129 W ,1.5 250C-2 Hours 83 101107 112 5.0 CR 2.4% 70 114 '5.0 3'. 250C-2 Hours 87 101 105 109 9 7.4L 1CR 4.4% 73 98 107 116 I 4.8 250C2 Hours 84 101 105 f 49 CR 6.8% 62 99108 118 4.0 250C-2 Hours 82 99 105 110 I ment of from 30 minutes to 8hours at temperatures be- 45 EXAMPLE ll tween 800C and 350C.

In the heat treatment steps generally longer times are used with lowertemperatures.

In addition to imparting improved 0.01 percent offset yield strength,the process of the present invention also obtains numerous advantages.The material of the present invention retains the finely structured coldworked matrix. In addition, the process of the present inventionmaintains and strengthens the deformation texture, resulting in improvedtexture strengthening of the sheet and formed part. Still further, theprocess of the present invention allows sufficient recovery of ductilityat ation. .The material thus produced in each cold recluc tion was givena second 2 hour anneal at 250C and the tensile properties for eachprocessing step are shownin w Table 11.

TABLE I1 -Continued Strengths in ksi Therefore it can be seen from theforegoing examples that the desirable high 0.01 percent offset yieldstrength is lost as a result of forming operations. In accordance withthe present invention even after small deformations resulting from theseoperations, the high 0.01 percent yield strength can be restored.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

1. A method for obtaining improved 0.01 percent offset yield strengthcharacteristics in copper or copper base alloy formed parts whichcomprises:

A. providing a copper base alloy material in plate form having athickness of from 0.300 to 1.800 inches;

B. cold rolling said material to a total reduction of at least 65percent;

C. heat treating said material at 100 to 350C for from 30 minutes to 8hours to decrease the tensile strength and increase the 0.01 percentoffset yield strength while retaining the cold worked matrix;

D. forming said material after said heat treatment step into a formedpart; and

E. heat treating the formed part at 100 to 350C for from 30 minutes to 8hours to decrease the tensile strength and increase the 0.01 percentoffset yield strength while retaining the cold worked matrix, therebyproviding a formed part having high yield strength characteristics.

2. A method according to claim 1 wherein step (B) includes cold rollingsaid material in at least two cold rolling cycles to a total reductionof at least percent with an intermediate heat treatment of from 100 to350C for from 1 to 4 hours between each cold rolling cycle provided thatthe rolling reduction in each cold rolling cycle is at least 25 percent.

3. A method according to claim 1 wherein the total reduction in step (B)is at least percent.

4. A method according to claim 2 wherein the total reduction in step (B)is at least 85 percent.

5. A method according to claim 4 wherein step (B) includes three coldrolling cycles with two intermediate heat treatment cycles.

6. A method according to claim 4 wherein step (B) includes two coldrolling cycles with one intermediate heat treatment cycle.

7. A method according to claim 1 wherein the starting material in step(A) is provided by hot rolling an ingot to plate form having a thicknessof from 0.300 to 1.800 inches. 7

8. A method according to claim 1 wherein said copper alloy is a phosphorbronze.

9. A method according to claim 1 wherein the copper alloy is anickel-silver.

10. A method according to claim 1 wherein said copper alloy containsiron in an amount of from 1 to 5 percent.

1. A METHOD FOR OBTAINING IMPROVED 0.01 PERCENT OFFSET YIELD, STRENGTHCHARACTERISTICS IN COPPER BASE ALLOY FORMED PARTS WHICH COMPRISES: A.PROVIDING A COPPER BASE ALLOY MATERIAL IN PLATE FORM HAVING A THICKNESSOF FROM 0.300 TO 1.800 INCHES; B. COOL ROLLING SAID MATERIAL TO A TOTALREDUCTION OF AT LEAST 65 PERCENT; C. HEAT TREATING SAID MATERIAL AT 100*TO 350*C FOR FROM 30 MINUTES TO 8 HOURS TO DECREASE THE TENSILE STRENGTHAND INCREASE THE 0.01 PERCENT OFFSET YIELD STRENGTH WHILE RETAINING THECOLD WORKED MATRIX; D. FORMING SAID MATERIAL AFTER SAID HEAT TREATMENTSTEP INTO INCREASE THE 0.01 PERCENT OFFSET YIELD STRENGTH WHILE REE.HEAT TREATING THE FORMED PART AT 100: TO 350*C FOR FROM 30 MINUTES TO 8HOURS TO DECREASE THE TENSILE STRENGTH AND INCREASE THE 0.01 PERCENTOFFSET YIELD STRENGTH WHILE RETAINING THE COLD WORKED MATRIX, THEREBYPROVIDING A FORMED PART HAVING HIGH YIELD STENGTH CHARACTERISTICS.
 2. Amethod according to claim 1 wherein step (B) includes cold rolling saidmaterial in at least two cold rolling cycles to a total reduction of atleast 70 percent with an intermediate heat treatment of from 100* to350*C for from 1 to 4 hours between each cold rolling cycle providedthat the rolling reduction in each cold rolling cycle is at least 25percent.
 3. A method according to claim 1 wherein the total rEduction instep (B) is at least 85 percent.
 4. A method according to claim 2wherein the total reduction in step (B) is at least 85 percent.
 5. Amethod according to claim 4 wherein step (B) includes three cold rollingcycles with two intermediate heat treatment cycles.
 6. A methodaccording to claim 4 wherein step (B) includes two cold rolling cycleswith one intermediate heat treatment cycle.
 7. A method according toclaim 1 wherein the starting material in step (A) is provided by hotrolling an ingot to plate form having a thickness of from 0.300 to 1.800inches.
 8. A method according to claim 1 wherein said copper alloy is aphosphor bronze.
 9. A method according to claim 1 wherein the copperalloy is a nickel-silver.
 10. A method according to claim 1 wherein saidcopper alloy contains iron in an amount of from 1 to 5 percent.